1. Field of the Invention
The present invention relates to a combustion-engined setting tool for driving fastening elements, primarily, in constructional components and including a fuel source, a combustion chamber, a fuel guide connecting the fuel source with the combustion chamber, at least one electronically controlled valve arranged in the fuel guide between the fuel source and the combustion chamber, and a control unit for opening the electronically control valve for a predetermined, by the control unit, time period.
2. Description of the Prior Art
Setting tools of the type described above operate on gaseous or liquid fuels which are combusted in the combustion chamber, driving the setting piston with which fastening elements are driven in.
Generally, with use of fuel, there exists a problem of admixing, for each operational cycle, a proper amount of air or oxygen, which is used as oxidation means, to the fuel. In particular, air, when taken from a surrounding environment, is subjected to pressure and temperature fluctuations which unfavorably influence the combustion of the air-fuel mixture, in particular when the fuel content in the mixture is too large or too small.
European Publication EP 0 597 241 B1 discloses a combustion-engined setting tool in which fuel is fed from a fuel source to the combustion chamber through a normally-closed solenoid valve. The solenoid is excited electronically, with the excitation being controlled by a switching circuit. The switching circuit opens the solenoid valve for a predetermined, adjustable time period in response to closing of an actuation switch. During this time period, fuel flows from the fuel source into the combustion chamber. The drawback of this tool consists in that the process of filling the combustion chamber starts only after the tool has been pressed against a constructional components into which a fastening element is to be driven, and the switch is actuated. This leads, in particular at low environmental temperatures, to a noticeable increase of the time period during which the combustion chamber is filled with fuel, which slows the setting process.
German Publication DE 42 43 617 A1 discloses a combustion-engined setting tool in which during an operational cycle, a gas inlet valve is mechanically opened and through which fuel flows from a fuel source into a storage chamber that communicates with the environment. Due to this communication, the pressure and, if necessary, the temperature can be balanced with the environmental air, so that a proper air-fuel mixture is fed into the combustion chamber. The mixture is fed from the storage chamber into the combustion chamber by a predetermined time. The drawback of the setting tool of DE 42 43 617 A1 consists in increased fuel losses.
Accordingly, an object of the present invention is to provide a setting tool in which the drawbacks of the prior art setting tools are eliminated.
Another object of the present invention is to provide a setting tool of the type described above with which rapidly following one another, setting processes can be effected.
A further object of the present invention is to provide a setting tool of the type described above and in which an optimal fuel metering becomes possible.